FREEHOLD — Shocking new details were revealed at a detention hearing for Liam McAtasney, the 19-year-old Neptune City man charged with killing Sarah Stern.

At a detention hearing on Tuesday morning in Freehold, Judge David Bauman ruled that McAtasney, 19 would remain in custody until his trial.

Assistant Prosecutor Meghan Doyle said McAtasney admitted to murdering Stern on Dec. 2 "by his own hands" by choking her — an admission secretly video-recorded in a conversation with a friend identified only as "A.C."

In the conversation, McAtasney described how he strangled Stern to death, lifted her in the air and "then left her on the floor and watched her die for 30 minutes," Doyle said.

"He knew exactly how long it was because he chose to time that," Doyle said.

Doyle said that after the murder, McAtasney spend the next two months "calculating every one of his moves to continue to cover up the murder and death of Sarah Stern. He lied to police. He conducted a search with friends and family of Ms. Stern because he thought that that would alleviate his guilt. He admitted that he pretended to make their friendship more than it was so that people would not focus on him as a suspect."

Authorities say that after the killing, McAtasney contacted friend Preston Taylor, and together they moved and disposed of her body eight hours after she was strangled.

Monmouth County Prosecutor Christopher Gramiccioni has said McAtasney allegedly drove an Oldsmobile belonging to Stern’s grandmother to the a Route 35 bridge with Taylor following in another vehicle. Together they threw the body off the bridge, according to Gramiccioni.

Video of a police officer finding the abandoned car was released this week:

At Taylor's detention hearing last Tuesday, Doyle said McAtasney planned to rob and kill Stern's for six months.

Prosecutors have said Taylor led investigators to safes buried in Sandy Hook and Shark River Park, containing money and Stern's clothing.

After the hearing McAtasney's lawyer told reporters that his client did not hurt Stern "and wouldn't hurt her."